As we grow up our sleep behavior changes. In our
teens, we need lots of sleep and getting us out of bed in the mornings is not
an easy task. This is not made any easier by the tendency of the young to be
semi-nocturnal – a habit that can last until they should all know better. Of
course, way back in our evolutionary infancy, we were nocturnal little primates
doing our best not to get swallowed up by the large predatory beasts out there.
As the ancestral primates of 50 to 60 Myr ago came
out of the dark, they developed a wide range of social structures running the
gamut of solitary individuals through single male polygamous groups to large
social groups. There have been a couple of theories as to how the social groups
developed. Shultz and her colleagues have published the results of a computer
simulation that seems to fit the bill better than previous pictures (1).
The benefits of daytime foraging are
counterbalanced by the increased risk of being spotted and ending up as someone
else’s breakfast. The simulation
predicts that the predation risk would be lessened by loose aggregates of the
emerging primates. Further cohesion into large cooperative social groups would
further enhance this benefit.
Better foraging results and better protection against
predation then leads to more babies and expanding populations. So it seems that
social living resulted from giving up the night shift and didn’t appear to have
anything to do with looking around for sexual partners.
It seems somewhat ironic that after almost 20 Myr
of evolution, our younger generation should seem to be so in love with the
nocturnal lifestyle.
